From fcb2bf280573ef275c8004eb2a91490c9ff9d095 Mon Sep 17 00:00:00 2001
From: Nigel Banks <nigel.g.banks@gmail.com>
Date: Tue, 27 Aug 2013 23:41:57 +0200
Subject: [PATCH] Prevents a white screen when a viewer is set but not enabled.

If a user selects a viewer and then disables that module, but does
not change any solution packs viewers settings this can occur.
---
 includes/solution_packs.inc | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/includes/solution_packs.inc b/includes/solution_packs.inc
index a80c41a5..7cf0351a 100644
--- a/includes/solution_packs.inc
+++ b/includes/solution_packs.inc
@@ -745,7 +745,9 @@ function islandora_get_viewer($params = NULL, $variable_id = NULL, $fedora_objec
     $viewer_id = islandora_get_viewer_id($variable_id);
     if ($viewer_id AND $params !== NULL) {
       $callback = islandora_get_viewer_callback($viewer_id);
-      return $callback($params, $fedora_object);
+      if (function_exists($callback)) {
+        return $callback($params, $fedora_object);
+      }
     }
   }
   return FALSE;